The present invention relates, in general, to the construction of beams and more particularly, to a compound beam comprising a web plate consisting of a non-metalic material such as timber or of wood-based board and a flange affixed to at least one end thereof. This structure is particularly suited for use as a beam, rod or column, which will be subjected to, bending, tension or compressive stress or a combination thereof.
Various kinds of beams, columns or rods of timber construction utilizing a plate as their web component are commonly employed in the primary and secondary structures of buildings. Compound beams assembled from separate parts are in themselves known in prior art. They typically consist of a web plate and of timber flanges attached thereto by glue, nails or screws. The attachment of the flange to the web plate is accomplished by glueing alone or in combination with nails or screws, and the pressing which the glue requires during its curing period is accomplished in a press or by means of nails or screws.
In the German application prints No. 2 021 028 and 2 042 800, examples are disclosed of compound beam designs known in the art. The first of these publications discloses a timber beam, the deflection of which the deflection has been reduced by providing a metal strip on the side that will be subjected to tensile stress. This strip serves to take up the greater part of the tensile stress. It is also possible with the aid of this strip, to establish in the beam an existing stress, this being done by curving the timber beam before attaching the strip.
In the latter application print, a combination beam is disclosed in which the web consists of sheet metal and the flanges are timber strips attached thereto by nailing, for instance.
Numerous drawbacks are associated with the flanged beams of the prior art. In the case of beams composed of timber material alone, the major drawback in practice is connected with the deflections, among which in particular the vibration of the structural part due to moving loads is experienced as a factor seriously interfering with the comfort of living. in the case of long spans and prolonged loading, the relatively low rigidity and major creep of the timber give rise to objectionable deflections, which as a rule are clearly visible. Undesirable deformations, moreover are caused under variable humidity conditions by the sensitivity of timber to moisture, especially in box-type structures.
The massive character of the solid timber structures employed imposes extra load on other structural parts and implies uneconomic use of timber. Timber material is likewise wasted by present-day frame structure designs in load-bearing and non-bearing structures, especially in thick walls, and these designs are characterized by poor thermal economy. The use of a metallic web in a compound beam is also not recommended because a so-called cold bridge is established between different structural components.
Drawbacks are also encountered in the manufacturing of glued asemblies. Closely controlled plant conditions are required ro regulate humidity and temperature. In addition, close supervision of the process and pressing throughout the glue curing period is required. The manufacturing process, moreover, is labor-intensive.
Nailed joints can be made in plant facilitates or on site. But the drawback of this type of construction is that the number of nails required to insure a given strength tends to become unreasonably high, and thus compels the designer to increase the areas of components merely to provide space for placement of the nails. Nailing at too close a spacing causes checking of the timber. Furthermore, nailed joints are subject to creep under permanent load and give rise to deflections in the course of time. Nail plates are generally used when it is desired to mutually connect timber parts of a structure. The normal stresses are taken onto the wood, and the nail plate only operates as connector and transmitter of stresses. Attempts to place a stress on beams assembled with timber have not been successful to date.